This invention relates generally to a casting method and, more specifically, to an improved full mold casting method using a consumable pattern which in shape is an exact replica of the intended casting and which is vaporized and displaced by a molten metal charge.
There is known a full mold casting method including the steps of surrounding a consumable pattern formed of an expanded plastic material with particulate refractory material, vaporizing the pattern by contacting the pattern with molten metal, and filling the resulting cavity with the molten metal. As the consumable patterns, those formed of expanded polystyrene resins have been conventionally used. Because of the presence of benzene rings having a relatively high bond dissociation energy, however, the polystyrene resins are incapable of being perfectly decomposed and volatilized and have a tendency to leave a residue. The residue from incompletely destroyed pattern causes surface defects such as dirt, carbon deposit, wrinkles and roughness, and inside defects such as carburization. Therefore, the resulting castings having such defects require additional surface finishing works or must be rejected.
The present invention has been made with a consideration of the above-described problems encountered in the conventional full mold casting method.